Antoine Equation • NIST-Verified Constants
Select a compound to see Antoine constants.
Constants are verified against NIST Chemistry WebBook.
Understand vapor pressure principles, Antoine equation, VLE calculations, and engineering applications
Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid at a given temperature. It's fundamental to VLE calculations, distillation design, and safety relief sizing. At the normal boiling point, vapor pressure equals 1 atm (760 mmHg).
At the normal boiling point, P = 760 mmHg (1 atm). Use this to verify calculations.
| Compound | NBP (°F) | NBP (°C) | Typical Use |
|---|---|---|---|
| Propane | -44 | -42 | LPG, refrigerant R-290 |
| n-Butane | 31 | -0.5 | LPG, aerosol propellant |
| n-Pentane | 97 | 36 | Gasoline blending, blowing agent |
| n-Hexane | 156 | 69 | Extraction solvent |
| n-Heptane | 209 | 98 | Octane rating reference (0) |
| n-Octane | 258 | 126 | Gasoline component |
| Methanol | 149 | 65 | Hydrate inhibitor, fuel |
| Ethanol | 173 | 78 | Fuel additive, solvent |
| Water | 212 | 100 | Process steam |
The Antoine equation calculates vapor pressure as log₁₀(P) = A − B/(C + T), where P is vapor pressure in mmHg, T is temperature in °C, and A, B, C are compound-specific constants. This calculator uses NIST-verified constants for hydrocarbons C3-C8, alcohols, and water.
Vapor pressure determines whether a liquid will vaporize at given conditions, which is critical for storage tank vent sizing per API 2000, pump NPSH calculations, flash point assessment, and two-phase flow predictions in pipelines.
Reid Vapor Pressure is the vapor pressure of a liquid measured at 100°F (37.8°C) per ASTM D323. It is the standard specification for gasoline volatility, NGL product quality, and crude oil storage classification.
The Antoine equation provides ±1-3% accuracy within the valid temperature range for each compound. Extrapolation beyond the published range significantly decreases accuracy, and critical applications should verify results with equation of state models.